NSRRC Activity Report 2023

Soft Matter 043 Ru-Jong Jeng (National Taiwan University) and his team recently developed a green process for preparing recyclable PU/silica (PU/SiO 2 ) nanohybrids as gas separation membranes for CO 2 capture and storage ( Fig. 1 ). By using the heterofunctional reagent (3-aminopropyl)triethoxysilane (APTES) as an aminolysis agent, PC waste was selectively decomposed into key intermediates containing the versatile functional groups of active hydrogens and alkoxysilanes. One pot synthesis of PU/SiO 2 nanohybrids was achieved through click reactions with active hydrogens and subsequent sol–gel reactions of alkoxysilanes. Through the incorporation of key ingredients, such as poly(tetramethylene ether) glycol (PTMEG) or polycarbonate diols (PCDLs), PU/ SiO 2 hybrids with robust elastomeric properties was obtained. In addition, the presence of various SiO 2 particle sizes and microphase separation in these PU/ SiO 2 -based membranes resulting in improved CO 2 /N 2 selective gas permeation properties. Using recycled intermediates, their approach provided membranes with unique active sites (phenolic carbamate groups) that were recyclable even after consumption. PU/SiO 2 properties depend heavily on microphase separation morphology, which were analyzed using small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) at TLS 23A1 . The scattering peaks at 0.02–0.06 Å −1 (12–30 nm) signify long-range order between hard and soft segment domains in microphase separated structures with a large X-ray scattering contrast. For PU with poly(ethylene glycol) (PEG) diol samples, a well-mixed morphology without a significant domain size was observed in the SAXS measurement due to the partially soluble nature of PEG-based polyol in nanohybrids. In contrast, clear domain spacings were observed in the SAXS measurement for the nanohybrids composed of PTMEG or PCDL. These results suggest that the PTMEG-based and PCDL-based PU/SiO 2 nanohybrids exhibit morphologies with a larger extent of microphase separation, having more microcavities to facilitate diffusion of gas molecules, and thus leading to membranes with improved gas permeability. The microphase behavior of the PU/SiO 2 nanohybrids was also analyzed using WAXS. The characteristic scattering peaks of PEG (18.8° and 23.0°), PTMEG (19.5° and 24.0°), and PCDL (19.8° and 23.1°) crystallinity were observed before the sol–gel reaction. However, after the sol–gel reaction, all PU/SiO 2 nanohybrid samples only exhibited an amorphous phase signal because the sol–gel reactions hinder the crystallization of soft segments. This new PU/SiO 2 nanohybrid gas separation membrane has a high P CO2 permeability of 24.02 Barrer and a selectivity of 32.85 (α CO2/N2 ), which approaches the upper bounds reported by Robeson. 2−3 Moreover, the joint presence of polycarbonate polyol and silica in the nanohybrids led to strong elastomeric properties, with tensile strengths of 35.5 MPa and over 700% elongation at the breaking point, exceeding those of previously reported PU-based gas separation membranes. The newly developed PC recycling process featured carbamate groups as the reaction sites, enabling the recycled PU/SiO 2 nanohybrids to be used as gas separation membranes for CO 2 capture and storage. In the traditional linear economy model, any membrane application can only be discarded as polymer waste after it has become ineffective. This study introduces the concept of a circular economy, and a wide range of advanced applications involving CO 2 reuse is within reach. (Reported by Orion Shih) This report features the work of Ru-Jong Jeng and his collaborators published in J. Chem. Eng. 452 , 139262 (2023). TLS 23A1 Small/Wide Angle X-ray Scattering • SAXS and WAXS • Chemistry, Materials Science, Green Sustainable Chemical Process References 1. Y.-C. Huang, L.-F. Chen, Y.-H. Huang, C.-C. Hu, C.-H. Wu, R.-J. Jeng, J. Chem. Eng. 452 , 139262 (2023). 2. L. M. Robeson, J. Membr. Sci. 62 , 165 (1991). 3. L. M. Robeson, J. Membr. Sci. 320 , 390 (2008). Fig. 1 : Conceptual diagram of the CO 2 carbon cycle. PC: polycarbonate; PCDL: polycarbonate diol; PU: polyurethane. [Reproduced from Ref. 1]